Regular expressions in which PHP matches consecutive numbers or letters

Regular expression rules: "/Rules need to be written in the middle of 2 slashes/".

(.: decimal point) is used to match all characters except the line break.

(\s: Backslash lowercase s) is used to match a single space character, including the TAB key and line break;

(\s: The backslash capital S) is used to match all characters except a single space character;

(\d: Backslash D) is used to match numbers from 0 to 9, or it can be written like this: [0-9]

(\w: Backslash lowercase w) used to match letters, numbers, or underscore characters;

(\w: The backslash capital W) is used to match all characters that do not match the \w;

Meta characters include: +, *,?

Meta-characters are confusing to understand, so I did the code results later

The "+" metacharacters stipulate that their leading characters must appear consecutively or multiple times = For example,/es+/matches the "Tesseessssseast12354haeasashaha" string, first to match the first letter e, and then to match the s,s must appear one or more times, see the instance. The "*" meta-character specifies that its leading character must appear 0 or more times = For example,/es*/matches the "Tesseessssseast12354haeasashaha" string, first with the first letter E, the following s appearing 0 times, or in succession, to see the instance. “?” Metacharacters stipulate that their leading objects must appear consecutively 0 times or once = For example/es?/matches the "Tesseessssseast12354haeasashaha" string, first with the first letter E, The following s appear 0 times or at most once (that is, the last letter S does not recur).

Example code:

$str = "Tesseessssseast12354haeasashaha"; echo "=====". $str. " "; echo "/es+/:". Preg_replace ("/es+/", "-\\0-", $str). " "; echo "/es*/:". Preg_replace ("/es*/", "-\\0-", $str). " "; echo "/es?/:". Preg_replace ("/es?/", "-\\0-", $str). " ";?>

Execution Result:

Also if you feel the meta-character "+*?" "It is difficult to understand that this {} method can be used instead:

For example es* we can write es{0,}, and es+ we can write es{1,},es? can be written as es{0,1}, note: Do not write (and no spaces) when you are unsure.

Of course we have to specify how many times it can be written like this: es{3} means S appears 3 times

Extrapolate

For example, to replace a continuous number of spaces for a single space, I can write: Preg_replace ("/\s+/", "", $str);
For example, to find the number in the string (integer): Preg_replace ("/\d+/", "(\\0)", $str); \\0 is a string value that represents a conforming rule

For example, to find the number with a decimal point in the string: Preg_replace ("/\d+\.\d+/", "(\\0)", $str); Here's the "\." Indicates the output decimal point

Find a string consisting of letters: Preg_replace ("/[a-za-z]+/", "(\\0)", $STR)

Find a string consisting of (Letters, numbers mixed): Preg_replace ("/([a-za-z]|\d) +/", "(\\0)", $STR)

The "or" operation in the regular expression, using the "|"

For example, the above example: Find a string ([a-za-z]|\d) consisting of a mixture of (letters or numbers) ([a-za-z]|[ 0-9])

"^" is considered a negation operator when it appears in [], and [^0-9] represents any character except a number.

When "^" is outside the "[]" or "[]", it should be treated as a locator.

A locator means, for example: "^the": The first must have "the" string, similar: "en$": the $ symbol must be the end of en.

In fact, you will find the regular expression is very simple, unless I wrote the tutorial really have a problem.